All of the products currently on the market or known to be under development are being developed by European companies. The market leader is Robur, with ammonia-water absorption heat pumps available in air, water and ground source versions with nominal heat output around 40kW. GUEs in the different versions are higher than competitors. Water at up to 70 degrees Celsius can be produced but the GUE under these conditions is generally not available. A half-size version is under development. The present machines are single outdoor packages. Vaillant and Viessmann have water-zeolite adsorption machines on and near-market respectively. They are single indoor units, large in size, and when in heat pumping mode cannot produce water hotter than 55 degrees C. They use solar heated water (Vaillant) or ground source heat, air source being unfeasible with water as a refrigerant. Viessmann are developing a much more compact absorption machine, thought to use methanol as a refrigerant and capable of operating with air as a heat source. Other adsorption developments are in progress but further away from market. Improvements are needed in size and capital cost to achieve sales, but the efficiencies achieved by Robur are probably sufficient at least in the short term
